Methods of making paper tissue, towel, and the like are well known, including various features such as Yankee drying, throughdrying, fabric creping, dry creping, wet creping and so forth. Conventional wet pressing processes have certain advantages over conventional through-air drying processes including: (1) lower energy costs associated with the mechanical removal of water rather than transpiration drying with hot air; and (2) higher production speeds which are more readily achieved with processes which utilize wet pressing to form a web. On the other hand, through-air drying processing has been widely adopted for new capital investment, particularly for the production of soft, bulky, premium quality tissue and towel products.
Fabric creping has been employed in connection with papermaking processes as a means to influence product properties. See U.S. Pat. Nos. 4,689,119 and 4,551,199 of Weldon; U.S. Pat. Nos. 4,849,054 and 4,834,838 of Klowak; and U.S. Pat. No. 6,287,426 of Edwards et al. Operation of fabric creping processes wherein the creping is carried out at elevated web consistencies has been hampered by the difficulty of effectively transferring a web of high or intermediate consistency (30-60%) to a dryer. Note also U.S. Pat. No. 6,350,349 to Hermans et al. which discloses wet transfer of a web from a rotating transfer surface to a fabric. Further patents relating to fabric creping more generally including rush transfer or low consistency (i.e. 10-30%) fabric creping the following: U.S. Pat. Nos. 4,834,838; 4,482,429 4,445,638 as well as 4,440,597 to Wells et al. where rush transfer of a web at consistencies of about 10 to 30 percent is described.
Throughdried, creped products are disclosed in the following patents: U.S. Pat. No. 3,994,771 to Morgan, Jr. et al.; U.S. Pat. No. 4,102,737 to Morton; and U.S. Pat. No. 4,529,480 to Trokhan. The processes described in these patents comprise, very generally, forming a web on a foraminous support, thermally pre-drying the web, applying the web to a Yankee dryer with a nip defined, in part, by an impression fabric, and creping the product from the Yankee dryer. A relatively permeable web is typically required, making it difficult to employ recycle furnish at levels which may be desired. Transfer to the Yankee typically takes place at web consistencies of from about 60% to about 70%.
As noted in the above, throughdried products tend to exhibit enhanced bulk and softness; however, thermal dewatering with hot air tends to be energy intensive and requires a relatively permeable web, such that recycle fiber is difficult to process in this manner. Wet-press operations wherein the webs are mechanically dewatered are preferable from an energy perspective and are more readily applied to furnishes containing recycle fiber which tends to form webs with less permeability than virgin fiber. Wet press/wet or dry crepe processes have been employed widely as is seen throughout the papermaking literature. Many improvements of wet-press processes relate to increasing the bulk and absorbency of compactively dewatered products.
As an alternative to conventional wet-press and throughdrying processes, attempts have been made to incorporate air-pressing technology into papermaking machines. See, for example, the following patents of Hermans et al.; U.S. Pat. Nos. 6,497,789; 6,454,904; 6,096,169; and 6,083,346. Note, also, the following patents: U.S. Pat. Nos. 6,579,418; 6,318,727; 6,306,258; 6,306,257; 6,280,573; 6,338,220; 6,143,135; 6,093,284; and 6,080,279.
However, it is found that sealing of the press and/or channeling of the web limits the utility of proposed systems. Moreover, wet pressing in connection with air pressing during production may result in relatively dense webs unless great care is taken to avoid densification.